I tried to measure my B&W803 Nautilus with Sofmea. Here is the result below (unsmoothed) :

It is possible to compare this result with the one from Arta (smoothed 1/12e octave). As you can see the result is quite similar.

First impressions are that the frequency response is quite linear with some small +/- 1 dB variations. Bass and tweeter above 5kHz seem to be just above the average level, but eventhough the box seem to be very well balanced...